Why kilometres to miles
Race distances (5K, 10K, half marathon), car speedometers and map apps outside the US and UK work in kilometres, while American and British readers think in miles. One kilometre is about 0.621371 miles, so a 10 km run is a little over 6.2 miles.
The mile used here is the international mile of exactly 1,609.344 m, agreed in 1959. Nautical miles (1,852 m) and the old US survey mile are different units.
Worked example
A half marathon is 21.0975 km: 21.0975 ÷ 1.609344 = 13.1093796 mi, which is why it is advertised as 13.1 miles.
Quick mental conversion
Multiply by 0.6 and add 3% of the original: 50 km → 30 + 1.5 = 31.5, against the exact 31.0686 mi. For distances under 100 km that rule is within about 2%.
How this works
The page divides by the exact factor:
mi = km ÷ 1.609344
Division by an exact decimal gives a repeating fraction, so the result is computed in double precision and cleaned of floating-point noise beyond 15 significant digits. The display uses the precision you pick (6 significant figures by default); Copy result copies the full value.
Frequently asked
How many miles are in a kilometre?
0.621371192 miles. It is the reciprocal of the exact definition 1 mi = 1.609344 km.
How far is a 5K in miles?
5 km is 3.10686 miles, usually quoted as 3.1 miles.
Is a nautical mile the same?
No. A nautical mile is exactly 1.852 km and is used at sea and in aviation; this page uses the statute (international) mile.
Is anything I type sent to a server?
No. The conversion runs in your browser and works offline.
Sources
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- Federal Register 59-5442 (1959) — Refinement of values for the yard and the pound
- Wikipedia — Conversion of units of length
Reviewed Oct 17, 2026 · test vectors fixtures/units/length/km-to-miles/